Combustor oscillating pressure stabilization and method

Abstract

High dynamic pressure oscillations in hydrocarbon-fueled combustors typically occur when the transport time of the fuel to the flame front is at some fraction of the acoustic period. These oscillations are reduced to acceptably lower levels by restructuring or repositioning the flame front in the combustor to increase the transport time. A pilot flame front located upstream of the oscillating flame and pulsed at a selected frequency and duration effectively restructures and repositions the oscillating flame in the combustor to alter the oscillation-causing transport time.

What is claimed is: 
     
       1. Improved apparatus for the active control of unstable oscillation-producing combustion in a combustion system comprising a combustion chamber having a combustion zone with opposite end regions and means for introducing a first mixture of a fuel and oxidizer into the combustion zone at one end region thereof for the combustion of the fuel and oxidizer mixture, wherein the combustion of the fuel and oxidizer mixture forms an oscillating flame within the combustion zone at a location intermediate said end regions to effect the formation of dynamic pressure oscillations within the combustion chamber with the amplitude of said oscillations being dependent upon the degree of an in-phase relationship of the pressure wave produced by each oscillation with the periodic heat release produced by the combustion of the fuel in said fuel and oxidizer mixture, the improved apparatus defined by combustion oscillating pressure stabilizing means for reducing the amplitude of the pressure oscillations within the combustion chamber and comprising, chamber means communicating with said combustion chamber at said one end region thereof, fuel supplying means and oxidizer supplying means coupled to one of said chamber means and said combustion chamber for introducing thereinto at least one flowing stream of fuel and oxidizer for forming a second mixture thereof for producing a pilot flame within said combustion zone at said one end region thereof, and flow control means for intermittently interrupting the flow of at least one of the fuel from the fuel supplying means and the oxidizer from the oxidizer supplying means into the chamber means at a selected frequency and duration for intermittently and sequentially interrupting and establishing the flow of said at least one of the fuel from the fuel supplying means and the oxidizer from the oxidizer supplying means into said one of the chamber means and the combustion chamber for forming discrete mixtures of fuel and oxidizer from said second mixture which sequentially produce a pulsing pilot flame within said combustion zone for contact with the oscillating flame in the combustion zone, said control means providing a frequency and duration of interrupting and establishing the flow of said at least one of the fuel and the oxidizer adequate to provide the pulsing pilot flame with sufficient thermal energy within said combustion zone to effect the restructuring of the oscillating flame and thereby sufficiently repositioning the oscillating flame in the combustion zone to change the phase relationship of each pressure wave with the each periodic heat release away from an in-phase relationship therebetween for reducing the amplitude of the pressure oscillations. 
     
     
       2. In an improved combustion system as claimed in claim 1, wherein the pressure oscillations are at a frequency in the range of about 20 to 5000 Hz, and wherein the intermittent interruption of the flow of said at least one of the fuel from the fuel supplying means and the oxidizer from the oxidizer supplying means is provided at a frequency less than about one-half of the frequency of the pressure oscillations and in the range of about 1 to about 2500 Hz. 
     
     
       3. In an improved combustion system as claimed in claim 2, wherein the the flow of at least one of the fuel and oxidizer is introduced into said one of the chamber means and the combustion chamber for a duration in the range of about 0.1 millisecond to a time corresponding to one-half of the period of said selected frequency. 
     
     
       4. In an improved combustion system as claimed in claim 1, wherein the pressure oscillations are at a frequency in the range of about 150 to 1200 Hz, and wherein the intermittent interruption of the flow of said at least one of the fuel from the fuel supplying means and the oxidizer from the oxidizer supplying means is provided at a frequency in the range of about 10 to 50 Hz. 
     
     
       5. In an improved combustion system as claimed in claim 4, wherein the the flow of at least one of the fuel and oxidizer is introduced into said one of the chamber means and the combustion chamber for a duration in the range of about 1.0 to 20 milliseconds. 
     
     
       6. In an improved combustion system as claimed in claim 1, wherein the ratio of the fuel to the oxidizer in said first mixture corresponds to a fuel equivalence ratio in the range of less than one to greater than about one, and wherein the ratio of the fuel to the oxidizer ratio in each of said discrete mixtures corresponds to a fuel equivalence ratio in the range of less than one to greater than one for providing fuel-lean to fuel-rich pulses of the pilot flame, and wherein the duration of the introduction of said at least one stream increases as the fuel equivalence ratio in said discrete mixtures decreases in said range of less than one to greater than one. 
     
     
       7. In an improved combustion system as claimed in claim 1, wherein said at least one stream comprises separate streams of fuel and oxidizer or a combined stream of fuel and oxidizer, and wherein means are provided for introducing said at least one stream formed of the oxidizer from the oxidizer supplying means and the fuel from the fuel supplying means into said one of the chamber means and the combustion chamber along a path separate from said first mixture. 
     
     
       8. In an improved combustion system as claimed in claim 7, wherein the fuel supplying means comprises first conduit means coupled to said chamber means, wherein the oxidizer supplying means comprises second conduit means coupled to said chamber means, and wherein said flow control means comprises valve means in at least one of said first and said second conduit means and valve control means for moving said valve means between open and closed positions at a frequency and duration sufficient to intermittently establish the flow of said least one stream of fuel and the oxidizer for pulsing the pilot flame in said combustion zone at the selected frequency and duration adequate to effect said restructuring and repositioning of the oscillating flame in the combustion chamber. 
     
     
       9. In an improved combustion system as claimed in claim 8, wherein said valve control means includes selectively adjustable means for controlling and varying the frequency and duration at which the pilot flame is pulsed. 
     
     
       10. In an improved combustion system as claimed in claim 9, where the ratio of the fuel to the oxidizer in said first mixture corresponds to a fuel equivalence ratio in the range of less than one to greater than about one and provides for the generation of the pressure oscillations in the combustion zone at a frequency in the range of about 150 to 1200 Hz, wherein the ratio of the fuel to the oxidizer ratio in each of said discrete mixtures corresponds to a fuel equivalence ratio in the range of less than one to greater than one for providing fuel-lean to fuel-rich pulses of the pilot flame, wherein said valve means are in said first conduit means, and wherein the selectively adjustable means intermittently interrupt the flow of the fuel from the fuel supplying means to the chamber means to pulse the pilot flame at a frequency less than about one-half of the frequency of the pressure oscillations and in the range of about 1 to about 2500 Hz and for a duration in the range of about 0.1 millisecond to a time corresponding to one-half of the period of said selected frequency. 
     
     
       11. In an improved combustion system as claimed in claim 10, wherein said valve means comprises fuel injector means, wherein the valve control means includes means responsive to an electrical signal for operating the fuel injector means, and wherein the selectively adjustable means comprises signal generating means for producing a series of discrete electrical signals for operating the fuel injector means at the selected frequency and duration. 
     
     
       12. In an improved combustion system as claimed in claim 9, where the ratio of the fuel to the oxidizer in said first mixture corresponds to a fuel equivalence ratio in the range of less than one to greater than about one and provides for the generation of the pressure oscillations in the combustion zone at a frequency in the range of about 150 to 1200 Hz, wherein the ratio of the fuel to the oxidizer ratio in each of said discrete mixtures corresponds to a fuel equivalence ratio in the range of less than one to greater than one for providing fuel-lean to fuel-rich pulses of the pilot flame, wherein said valve means are in said second conduit means, and wherein the selectively adjustable means intermittently interrupt the flow of the oxidizer from the oxidizer supplying means to the chamber means to pulse the pilot flame at a frequency at a frequency less than about one-half of the frequency of the pressure oscillations and in the range of about 1 to about 2500 Hz and for a duration in the range of about 0.1 millisecond to a time corresponding to one-half of the period of said selected frequency. 
     
     
       13. In the operation of a combustion system comprising a combustion chamber having a combustion zone with opposite end regions and fuel and oxidizer delivery means for forming and introducing a first mixture of fuel and oxidizer into the combustion zone at one end region thereof for the combustion of the first mixture of the fuel and oxidizer whereby the combustion of the first mixture produces an oscillating flame within the combustion zone at locations intermediate said end regions to effect the formation of dynamic pressure oscillations within the combustion chamber at a frequency in the range of about 20 Hz to about 5000 Hz, wherein the amplitude of each of the oscillations being dependent upon the degree of in-phase relationship of the pressure wave produced by each oscillation with the periodic heat release produced by the combustion of the first fuel and oxidizer mixture, the method for reducing the amplitude of the oscillations within the combustion chamber by the steps comprising: forming a second mixture of fuel and oxidizer from separate flows of fuel and oxidizer, introducing the second mixture into said combustion zone at a location adjacent to said one end region thereof for producing a pilot flame within said combustion zone at said one end region thereof; and, intermittently interrupting the flow of at least one of the fuel and the oxidizer forming said second mixture or the flow of the second mixture to produce discrete charges of the second mixture for intermittently interrupting and establishing the pilot flame within the combustion zone at a rate and for a duration adequate to produce sufficient thermal energy within said combustion zone for sufficiently restructuring the flame in the combustion zone and thereby repositioning the flame in the combustion zone with respect to said location for changing the phase relationship of each said pressure wave to each periodic heat release with respect to said in-phase relationship and thereby reducing the amplitude of the pressure oscillations in said combustion chamber. 
     
     
       14. In the operation of a combustion system as claimed in claim 13, wherein the rate of intermittently interrupting the flow of said at least one of the oxidizer and the fuel defining each of said discrete charges of the second mixture or the flow of the second mixture is at a selected frequency of less than about one-half of the frequency of the pressure oscillations and in the range of about 1 to 2500 Hz. 
     
     
       15. In the operation of a combustion system as claimed in claim 14, wherein the flow of at least one of the fuel and oxidizer defining each of said discrete charges of the second mixture or the flow of the second mixture is established between each interruption of said flow for a duration of about 0.1 milliseconds to a time corresponding to about one half of the period of said selected frequency. 
     
     
       16. In the operation of a combustion system as claimed in claim 13, wherein the ratio of the fuel to the oxidizer in said first mixture corresponds to a fuel equivalence ratio in the range of less than one to greater than about one, and wherein the ratio of the fuel to the oxidizer ratio in each charge of said second mixture corresponds to a fuel equivalence ratio in the range of less than one to greater than one for providing fuel-lean to fuel-rich pulses of the pilot flame, and wherein the duration of the flow of at least one of the fuel and oxidizer forming each charge of the second mixture or the flow of the second mixture increases as the fuel equivalence ratio in said second mixtures decreases in said range of less than one to greater than one. 
     
     
       17. In the operation of a combustion system as claimed in claim 13, wherein the step of intermittently interrupting the flow of at least one of fuel and the oxidizer and fuel to produce discrete charges of the second mixture is achieved by intermittently interrupting the flow of fuel forming the second mixture. 
     
     
       18. In the operation of a combustion system as claimed in claim 13, wherein the step of intermittently interrupting the flow of at least one of fuel and the oxidizer and fuel to produce discrete charges of the second mixture is achieved by intermittently interrupting the flow of oxidizer forming the second mixture. 
     
     
       19. In the operation of a combustion system as claimed in claim 13, wherein the step of intermittently interrupting the flow of at least one of fuel and the oxidizer and fuel to produce discrete charges of the second mixture is achieved by intermittently interrupting the flow of the fuel and the flow of the oxidizer forming the second mixture. 
     
     
       20. In the operation of a combustion system as claimed in claim 15, the additional step comprising generating a series of discrete electrical signals for selectively interrupting and establishing the flow of at least one of fuel and oxidizer forming each of discrete charges of the second mixture or the flow of the second mixture at said selected frequency and said duration. 
     
     
       21. In the operation of a combustion system as claimed in claim 15, wherein the pressure oscillations are at a frequency in the range of about 150-1200 Hz, and including the additional step comprising generating a series of discrete electrical signals for selectively interrupting and establishing the flow of at least one of fuel and oxidizer forming each of discrete charges of the second mixture or the flow of the second mixture at a frequency in the range of about 10 to 50 Hz and sufficient to interact with the frequency of the signals for adequately pulsing the pilot flame for effecting the restructuring and repositioning of the oscillating flame front away from said locations in the combustion zone where the pressure wave of each combustion oscillation is in or near an in-phase relationship with the heat release produced during each combustion oscillation. 
     
     
       22. In an improved combustion system as claimed in claim 13, wherein the fuel and oxidizer forming said second mixture is of a volume corresponding to about 2-20 percent of the volume of the fuel and oxidizer in said first mixture.